44 pages • 1 hour read
Zoë SchlangerThe Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth
Nonfiction | Book | Adult | Published in 2024A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 6-8Chapter Summaries & Analyses
Chapter 6 Summary: “The (Plant) Body Keeps the Score”
Historically, consciousness has been associated with memory and the ability to make decisions from it. The word “intelligence” is derived from the Latin root interlegere, which means “to choose between.” In this chapter, Schlanger turns her attention to what plants do with the information they take in and whether they store it in something akin to memory. She opens with Nasa poissoniana, a plant studied by researcher Tilo Henning in Berlin. Henning observed that the plant had memories, although where those memories are stored remains a mystery.
Nasa poissoniana exhibits the ability to count and remember time intervals. Most flowers are highly protective of their pollen, calculating its release based on a variety of factors. To increase the spread of its pollen, a flower will dole out on a small bit at a time to pollinators. However, Nasa poissoniana can detect if there are fewer pollinators than normal in the environment and release large amounts of pollen to guarantee greater distribution. The plant will also dilute nectar, causing pollinators to make multiple visits, thereby further increasing the spread of pollen. Even more striking is how the plant tricks pollinators: A bee that finds no nectar in one flower will not investigate the plant’s other flowers, but Nasa poissoniana will shoot out additional pollen so the bee will still carry some away.
Researchers discovered that the plant seemed to anticipate the arrival of the returning pollinator, shooting out its stamen just a few moments before the pollinator arrived. Experimentation revealed that the plant was counting, keeping track of time, and adjusting its pollen release to match the rhythms of its pollinators. In short, the plant was remembering the past and using that experience to make decisions about the future.
Schlanger explains that this idea of remembering and making decisions from memory is core to how humans think about their own consciousness. Yet, plants have long exhibited the ability to remember through vernalization. They can determine how much time has elapsed during cold periods to decide when to emerge, even distinguishing between warm spells and spring natural warming.
Researchers in human and animal neuroscience have not yet pinpointed exactly how memories are stored, and insight into plant memory is just as elusive. Animals’ memories are centralized in the brain, but plants appear to store memory throughout their bodies. Schlanger suggests that this difference may come down to the evolutionary impact of motion. For humans and animals who constantly on the move, having an organized, centralized, and portable way of processing the world makes sense. Plants, however, live stationary lives. Because of this, it is possible that they might use every component of their cellular structure to create and store memory.
Chapter 7 Summary: “Conversations with Animals”
Schlanger provides a synopsis of the 2018 novel Semiosis by Sue Burke. In the book, humans travel to another planet that is rich with plant life. However, they soon realize that they are far from the dominant species in this new world, and the only way to survive is to become servile to plants. Burke’s book presents a new way of thinking about the intrinsic relationship between animals and plants and how they communicate.
Schlanger investigates whether plant communication extends beyond plants themselves. While research into plant-to-plant communication has typically focused on stress or alerts of alarm, Schlanger asks what other information might be passed among plants or even to animals. This field of study is called biocommunication, and it reveals that that life on earth intermingles in complex ways. Schlanger reflects, “I get the sense that the rule of life is unruly mixture. Everything, it seems, is impacting and altering everything else” (138).
Ecologist Consuelo de Moraes discovered a bunch of crescent-shaped bites in the leaves of a plant in one of her experiments. She knew these bites were made by one thing: the bumblebee. However, bumblebees do not eat leaves. De Moraes determined that the bumblebees were starving; the flowers of the plant they fed on had not yet opened. In a controlled environment, De Moraes realized that the small bumblebee bites prompted the plant to produce flowers as many as 30 days before their natural cycle, providing the insects with what they needed. This benefitted the plant, too, by ensuring pollination.
This could be interpreted as a form of communication, and Schlanger asserts that what happened in De Moraes’s experiment happens across the plant kingdom in far more complicated ways. Goldenrods, able to sense gall-forming flies before they touch their petals, change their chemical compounds. Some plants hire ants to help stave off threats. For example, bittersweet nightshade emits tantalizing sugary nectar to invite ants to feed and help eliminate flea beetle larvae. Orchids mimic the body shapes of female wasps to entice male wasps to have sex with them, coating the wasps in pollen to be dispersed. However, research suggests that the flower’s shape has little to do with this trickery. Rather, the orchid flower releases highly specific chemical compounds designed to mirror the smell of specific species of female wasps.
Schlanger points to the work of botanist Robin Wall Kimmerer, a member of the Citizen Potawatomi Nation who details the unique symbiotic communication of all forms of life in her book, Braiding Sweetgrass. Kimmerer determines that the yellow-and-purple mixture of goldenrod and asters is designed to entice pollinators through the contrast of their colors. This mutuality among plants is well-known to farmers, who use companion crops to increase yield and stave off pests.
Much of this communication occurs using semiochemicals, synthesized compounds designed to be released and taken in by another. For example, birch trees growing near a plant called Labrador tea take in the plant’s chemical compounds and imbue their own leaves with its medicinal scent. Human influence and pollution have greatly impacted this form of chemical communication. Understanding how plants communicate and how human practices can negatively or positively affect this form of language could have profound implications for the future of the planet.
Chapter 8 Summary: “The Scientist and the Chameleon Vine”
Schlanger traveled to Chile to walk through the rain forest with a group of scientists. Her main interest was a singular vine called Boquila trifoliata that was said to exhibit biomimicry. Schlanger met with Ernesto Gianoli, the researcher who first discovered the vine’s unique ability. While walking through the forest, Gianoli noticed a boquila growing near a shrub. Where the vine grew along the tree, the leaves of the boquila mirrored the leaves of the tree. On each trip, Gianoli found the boquila performing this same artistry with a wide variety of plants. Some of the mimicries looked more like poor approximations than exact replicas, but the range of changes in the plant’s makeup showed a strong propensity for adaptive behavior.
Mimicry is nothing new in the plant world. The grains humans enjoy today—both rice and rye, for example—were first cultivated in wheat fields. Rice and rye mimicked the structure of wheat, cared for and spread by humans and animals. However, boquila’s mimicry was something new because it suggested something akin to vision is at play. The boquila’s mimicry caused many scientists to run with the idea that the vine could “see.” How else could the vine know how to copy the plants around it? One theory involves cyanobacteria; it argues that plants, having evolved from cyanobacteria—which have ocelli, or simple eyes that take in light information—have camera-like “eyes” in their leaves. Some argue that this explains why cells close to the outer edges of leaves do not contain chloroplasts, though this position would be most advantageous for taking in light.
Gianoli argues that while bacteria may play a role in boquila mimicry, it is not because the plant can “see.” He believes it more likely that horizontal gene transfer through bacteria or airborne chemical compounds is the catalyst for this change. However, anecdotal reports of boquila mimicking fake plants—and even Gianoli’s own research showing that if the host plant does not presently have any leaves, the boquila takes on its original form—suggest that more than chemistry is taking place. While on her trip with Gianoli, Schlanger noticed boquila imitating a fern—the first time this had been observed.
Chapters 6-8 Analysis
Schlanger continues to highlight the diversity of plant behaviors and responses while exploring new lines of inquiry into Plant Consciousness. Chapter 6 positions plant memory as a foundation for plant consciousness as it has long been considered central to human consciousness. This positioning is established in the title, “The (Plant) Body Keeps the Score,” which references The Body Keeps the Score by Bessel van der Kolk, a seminal book that explores how the human body stores trauma. This reference is another example of the way Schlanger blends disciplines to make her point and draw parallels between plants and humanity. In this case, she invokes the well-established concept that memory is not only a mental process but also something that affects and is stored in the body. She suggests that, like humans, plants respond to environmental stimuli in ways that indicate memory and adaptation. Schlanger uses the plant Nasa poissoniana, which can count and remember the time between pollinators and adjust its release of a pollen-laden stamen in anticipation of the next pollinator’s arrival, to illustrate this idea.
This example and others highlight the complexity of memory, taking it outside the realm of the central nervous system. Framing memory as an indicator of consciousness further blurs the lines between plants and humans. Schlanger writes, “Memories are the backbones of the narratives we tell ourselves about ourselves; nothing could be more essential to conscious experience” (123). She leans in to the similarities between plant and human consciousness, repeatedly reminding readers of their likenesses: Plants have circadian rhythms. Plants know how to wait. Plants correlate memory and movement just like humans.
However, Schlanger acknowledges that plant memory is not exactly like human memory, and scientists are still not sure where plant memory is stored. One theory is that a plant’s entire body is its “brain”—a complicated web of interactions and reactions driven by electrical waves and sensory information. Here, on a smaller scale, Schlanger points to The Complexity of Ecology, which is apparent even in the most minute processes of life. If a plant’s entire body is its brain, then that raises questions about the nature of human intelligence, consciousness, and the collective natures of memory and intelligence.
Another way that plants engage in complex, ecological exchange is through interspecies communication. As she discusses plant communication, Schlanger reminds readers that language matters. One paper published by Jarmo Holopainen describes plant communication as a form of “language” using “sentences” and “vocabulary.” This type of language tethers plant experience to the human experience, further supporting the possibility of Plant Consciousness.
Like with humans, plants’ biocommunication extends beyond their species, allowing them to exchange information with other forms of life. Holopainen suggests that plants essentially “talk” to other species. For example, corn, sensing the presence of caterpillars on its leaves, emits chemical compounds that attract the precise wasp needed to eradicate the infestation. Other plants draw ants in as bodyguards to keep pests away. Because they cannot change position, plants must find another way to respond to their environments. This interspecies communication shows plants’ ability to explore and enact solutions to external problems, which speaks to The Constant Motion of Biological Creativity.
Plants’ ability to adjust to their environment conflicts with long-held assumptions about plant life. Traditionally, plants have been considered stagnant forms of life restricted by the confines of their own genetic code. However, the examples Schlanger offers suggest that plants are highly adaptable, making decisions that have profound effects in milliseconds. Boquila trifoliata, the chameleon vine, reveals just how highly and quickly adaptable plants can be. Boquila mimics the leaves of plants around it to decrease the chance of it being digested. Boquila have even been documented mimicking invasive species that have been in the region for less than 10 years. This suggests that biological creativity and evolution works at a much faster pace than previously thought.
The boquila is central to Schlanger’s thesis, and it appears throughout the rest of the text. The plant’s adaptive and creative nature indicates a complex and nuanced engagement with its environment, one that may even be linked to something akin to vision:
Gianoli’s own work had shown that when the host tree was totally devoid of leaves, the vine leaves adopted their own normal, oval-shaped leaf morphology; plus, the vine leaves always mimicked the leaves closest to its own body, whether or not they were actually part of the climbed tree (173).
The boquila is important to Schlanger’s work because it continuously defies scientists’ expectations about how plants should and do behave. The debate about its ability to “see” is driven by the uniqueness of its adaptive qualities and defiance of scientific assumptions.
